Metal hyperaccumulation in the Brassicaceae species Arabidopsis halleri reduces camalexin induction after fungal pathogen attack

Abstract

Metal hyperaccumulation from the soil by certain plant species can serve as a defence trait. Such hyperaccumulation might impact the expression of organic defences. Here, the induction of the phytoalexin camalexin after leaf infection with a pathogenic fungus was investigated in plants of the facultative hyperaccumulator Arabidopsis halleri grown on unamended and metal-amended soil. Reduced camalexin induction was expected in plants grown in metal-amended soil. Plants were grown for twelve weeks on soil, which was either amended with high concentrations of Zn and Cd or kept unamended, and the final leaf concentration of Zn and Cd was determined. Conidia of the pathogenic fungus Alternaria brassicae were applied on mechanically damaged leaves. Leaves were harvested after 24 h and 48 h, and the amount of induced camalexin was quantified. Plants grown on metal-amended soil hyperaccumulated Zn and Cd and induced significantly less camalexin than plants grown on unamended soils after pathogen infestation. This suggests a physiological trade-off between metal hyperaccumulation and an induced antifungal organic defence, which has, to our knowledge, not been observed before in A. halleri for other organic defence compounds. This phenomenon might partly be explained by limitations in sulphur pools and/or the interruption of (phytohormonal) defence signalling due to metal hyperaccumulation. This work highlights the importance of considering defences elicited by antagonists from various guilds when studying plant organic defence responses to specific abiotic environments.